Sex-Linked Inheritance Problem Set

Problem 5: Another white-eyed female x red-eyed male fly cross

A white-eyed female fruit fly is crossed with a red-eyed male. Red eyes are dominant, and X-linked. What are the expected phenotypes of the offspring?

Tutorial

Genotypes and phenotypes of parents

The female parent must be homozygous because she has the recessive white-eyed phonotype.

The male parent is hemizygous, red-eyed.

Genotypes and phenotypes of offspring

All of the females eggs will contain an X chromosome with the white-eye mutation.

The sperm will contain either a normal X chromosome or a Y chromosome.

Summary

We use a punnett square to predict the outcome of this cross. Female offspring receive an X chromosome from both the sperm and egg. All females receive the dominant, red-eyed allele from their fathers and the recessive, white-eyed allele from their mothers.